The Z88 has several resistors and capacitors on the seriL port lines, presumably for EMI filtration. On earlier machines, these are soldered dead-bug style directly to the connector pins and shell, which makes my plan to re-wire it to RS-232 pinout a bit fussy. My newer-production Z88 has a small PCB soldered to the back of the DE-9 connector with the resistors and bypass/filter caps, which makes changing the pinout much easier to implement.
I have included KiCad projects for both the original pinout with a DE-9F and the RS-232 pinout with a DE-9M.
This is the initial version of this project, yet to be build and thus provided with no warranty, assurances, promises, rumors, innuendos, or otherwise implications about its functionality or fitness for purpose. I have ordered boards for both versions and will report back to the community on the ZX World forums, the Z88 Telegram channel, and likely the Vintage Computer Federation forum as well.